1. Field of the Invention
The present invention relates generally to air conditioning system monitoring and, more specifically, to monitoring and evaluating the performance and efficiency of chiller units.
2. Description of the Related Art
The energy cost of operating an air conditioning system of the type used in high-rise and other commercial buildings can constitute the largest single cost in operating a building. Yet, unbeknownst to most building managers, such systems often operate inefficiently due to undesirable operating conditions that could be corrected if they were identified. When such conditions are identified and corrected, the cost savings can be substantial.
The type of air conditioning system referred to above typically includes one or more machines known as refrigeration units or chillers. Chillers cool or refrigerate water, brine or other liquid and circulate it throughout the building to fan-operated or inductive cooling units that absorb heat from the building interior. In the chiller, the liquid returning from these units passes through a heat exchanger or evaporator bathed in a reservoir of refrigerant. The heat exchanger transfers the heat from the returning liquid to the liquid refrigerant, evaporating it. A compressor, operated by a powerful electric motor, turbine or similar device, compresses or raises the pressure of the refrigerant vapor so that it can be condensed back into a liquid state by water passing through a condenser, which is another heat exchanger. The condenser water absorbs heat from the compressed refrigerant when it condenses on the outside of the condenser tubes. The condenser water is pumped to a cooling tower that cools the water through evaporative cooling and returns it to the condenser. The condensed refrigerant is fed in a controlled manner to the evaporator reservoir. The evaporator reservoir is maintained at a pressure sufficiently low as to cause the refrigerant to evaporate as it absorbs the heat from the liquid returning from the fan-operated or inductive units in the building interior. The evaporation also cools the refrigerant that remains in a liquid state in the reservoir. Some of the cooled refrigerant is circulated around the compressor motor windings to cool them.
It has long been known in the art that certain operating parameters are indicative of chiller problems and inefficient operation. It has long been a common practice for maintenance personnel to maintain a log book in which they periodically record readings from temperature and pressure gauges at the condenser, evaporator and compressor. Some chiller units are even equipped with computerized logging devices that automatically read and log temperatures and pressures from electronic sensors at the condenser.
Practitioners in the art have recognized that certain operating parameters can be used to compute a measure of chiller efficiency. For example, in U.S. Pat. No. 5,083,438, entitled “Chiller Monitoring System,” it is stated that temperature and pressure sensors can be disposed in the inlet and outlet lines of a condenser and chiller unit to measure the flow rate through the chiller and the amount of chilling that occurs, and a sensor can be placed on the compressor motor to measure the power expended by the motor. From these measurements, an estimate of overall chiller efficiency can be computed.
Merely estimating chiller efficiency does not help maintenance personnel to improve efficiency or even recognize the true monetary cost of the inefficiency. For example, there are guidelines known in the art as to what operating ranges of a parameter are normal or acceptable and what ranges are indicative of correctable inefficient operation. Moreover, even if inefficient operation is recognized from abnormal temperature and pressure readings, there are few guidelines known in the art that maintenance personnel can use to diagnose and correct the cause of the inefficiency. Moreover, maintenance personnel must generally make personal, on-site inspections of the chiller and its log to gather the information. Sometimes considerable time can pass between such inspections.
It would be desirable to alert maintenance personnel to correctable chiller problems as soon as they occur and to provide greater guidance to such personnel for diagnosing and correcting problems. The present invention addresses these problems and deficiencies and others in the manner described below.